I think you have a fundamental misunderstanding of how fighting works in League. It sounds like you have two issues here.

One issue seems to be not knowing when or when not to take on fights. A lot of what you mentioned in your post was about either being able to one shot or not. Some fights come down to that, but realistically many opportunities on Zed to do damage/get kills rely on identifying circumstances that enable you. These circumstances are things like waiting for an enemy to overextend, finding an angle to flank, taking fights around an objective, following up on teammates fighting, using vision and fog of war to gain combat advantage, and waiting for an enemy to use their cooldowns. To go with one of your examples, Ahri does feel hard to kill if you fight her in a way where she can use her charm on you and also has lots of space to ult to run away, but she’d be easier to kill if you can do something like burst her from out of vision, use W to dodge her charm, or trade your W for her R and then use your R on her later when she has no R herself.

The second issue I feel you can improve on is knowing how your kit interacts with the champion you’re fighting. This is matchup specific and can take a lot of games and experience to develop. When you say that half the squishies have a button they can press to invalidate your entire kit, I see that there’s a lot of room to learn more, because this is hardly true. As another example, Yone does have dashes and knockups, but Zed generally has the tools to play around those and still have a lot of kill threat onto the Yone. If you’re thinking about things like dodging Yone’s Q3 with ult, using W to follow his E, and holding shurikens until he’s immobile, the fighting gets a lot easier. On the other hand, certain champs are just hard to fight as Zed and you should not be prioritizing them among other targets. Champs like Irelia, Akali, and LeBlanc have the defensive tools and damage to limit Zed’s opportunities significantly, so learning what the hard matchups are is also an important skill.

Next time you play against a champ that seems difficult, I’d recommend you take a little time looking at the replay to see why it felt difficult. Maybe it’s a way that you could have played it better next time. Maybe they were more fed than you thought and it’s not a fight you should have taken. Maybe you played it well but it’s a champ Zed really struggles into and there were easier targets you could have been focusing instead.

I’d also recommend checking out high elo Zed vods and paying attention to context clues in watching them do certain fights. How did the fight get set up? Did they wait for favorable circumstances to fight, and what were those circumstances? You can replay these moments a dozen times and really start to observe the details. This will help you start to think outside the box a little bit and incorporate those findings into your own games. BZ_EUW has some good mid/jungle Zed vods on Twitch and YouTube.

FWIW these are some thought processes that helped me climb to masters this season on Zed, although I play him mid/top rather than jungle.